Communications for the future

The Optics and Photonics Research Center at the State University of Campinas has taken a leadership role in studies related to Fiber Optic Parametric Amplifier technology.

By Claudia Izique

Agência FAPESP – The technology currently in use in optical communication networks will be unable to keep pace with the expanding demands of the Internet, mobile devices, high-definition television and the telecommunications industry expected over the next 20 years. Operating capacity, currently at one terabit per second, will need to be multiplied by a factor of between 100 and 1,000 to serve the ever-growing number of users – which will represent nearly half the world’s population by 2017 alone – along with global corporate traffic.

In a network-connected world, the collapse of communications would be a virtual apocalypse, and the search for solutions is mobilizing companies and research institutions such as the Optics and Photonics Research Center (CePOF) at the State University of Campinas (UNICAMP), one of the Research, Innovation and Dissemination Centers (RIDCs) funded by FAPESP. “We are conducting all kinds of optical communication studies, from characterizing fibers to testing the most advanced systems using first-world equipment,” says Hugo Fragnito, coordinator of the RIDC.

The RIDC has taken a leadership role in this global race with studies related to Fiber Optic Parametric Amplifier (FOPA) technology. Amplifiers serve to maintain the strength of the light signal that runs through the interior of the fibers, and parametric amplifiers may indeed be the answer to the challenge of increasing bandwidth and, as a result, network traffic. “We’ve set a record: we have already achieved a bandwidth of 115 nanometers (one nanometer equals one millionth of one millimeter),” he explains.

It was, in fact, an achievement: the systems that are currently available guarantee a maximum bandwidth of 30 nanometers in the area of optical communication and are capable of handling up to 80 lasers, which limits transmission to a few terabits per second. The greater the bandwidth, the higher the number of lasers placed on a single fiber and the greater the traffic capacity. “By using FOPAs, it will be possible to transmit ten times more,” explains Fragnito.

Certain problems still need to be solved before FOPAs can be launched on the market. The first is controlling light dispersion on the optical fiber, which is the result of variations in the fiber diameter along the route that could compromise the gains introduced by the new technology and thus limit the efficiency of the FOPA. “We’re studying how to develop extremely uniform fibers and waveguides to reduce fiber dispersion,” Fragnito adds.

The second problem, which is still unresolved, pertains to the size of the equipment. In the world of high technology, space is cost. The ideal would be to put “everything inside one chip,” says Fragnito. “Integrated optics has been driven by the need of the microelectronics industry to overcome the limits of physical space to increase performance rates. Today, we are betting on the miniaturization of fiber optics components, making everything smaller and cheaper.”

With funds from FAPESP, the CePOF has created a state-of-the-art infrastructure for manufacturing silicon-based integrated optical devices and other semiconductor materials. This technology will allow the integration of dozens of lasers, filters, detectors and other photonic devices interconnected by nanometer-sized waveguides in a single chip the size of a quarter.

Tellurite glass

The commercial operation of parametric amplifiers promises to promote a new revolution in optical communication, comparable to the erbium-doped fiber optics technology adopted in the mid-1990s. “Erbium made the Internet possible,” emphasizes Fragnito.

Before erbium, he says, fiber optic communication between São Paulo and Campinas worked at a maximum capacity of one gigabit per second, with one laser per fiber. If demand grew, it was necessary to install more fibers. Moreover, an electronic circuit repeater had to be installed every 20 kilometers to allow the light to travel unimpeded. In addition to being expensive, the system was slow.

Erbium, a rare-earth chemical element, can emit photons that increase light intensity. Together with wavelength division multiplexing (WDM) technology, it can transform a single fiber into a type of laser cluster that operates at different frequencies and with stronger signals. The new technology has made wide-bandwidth services viable and has enabled amplifiers installed every 50 kilometers along the fiber route to replace repeaters, accelerating data traffic. Given the risk of network congestion, however, the efficiency of the amplifiers, as well as all other optical network components, including fibers, must be ensured.

The optical fibers are manufactured with silicon, an oxide that is both abundant and cheap. The problem is that an optical amplifier carries 20-30 meters of rolled silicon fibers, which increases the size of the equipment. Researchers at the CePOF are investigating alternatives to this material and have achieved interesting results by replacing silicon with tellurium oxide via a technology that has, in fact, already been patented.

“The advantage of using tellurite is that it allows the erbium to dissolve at a concentration 70 times higher than silicon,” explains Fragnito. The presence of more erbium results in more photons and, consequently, more light. The use of tellurite may make it possible to reduce the length and the volume of the fibers and, consequently, the size of the amplifiers. “The current buzzword is miniaturization, reducing the size from 20 meters to mere centimeters,” he says.

To learn more about CePOF: The versatility of light, The KyaTera Network, an optical test platform, and Knowledge for society.